Adsorption systems in heatless fractionation processes



March 1, 1966 F. H. KANT ETAL 3,237,379

ABSORPTION SYSTEMS IN HEATLESS FRACTIONATION PROCESSES 5 Sheets-Sheet 1Filed Feb. 26, 1962 32 1 SECONDARY EFFLUENT PRIMARY 1 EFFLUENTABSORPTION SYSTEMS IN HEATLESS FRACTIONATION PROCESSES 5 Sheets-Sheet 2Filed Feb. 26, 1962 com 02. com 8 00 con 08 oo o m m n e V .m u m m n m.0 0 m M. H w N mSR fi wKd .GSH m w fim mm mHWCC o H V 2 w M G-m y EMLAKPatent Attorney GRAMS 0F COMPONENT ADSORBED PER IOO GRAMS OF ADSORBENTMarch 1, 1966 KANT ETAL 3,237,379

ABSORPTION SYSTEMS IN HEATLESS FRACTIONATION PROCESSES Filed Feb. 26,1962 5 Sheets-Sheet 5 FIG 3 NORMAL HEXAN'E 28 0N ACTIVATED CHARCOAL 24NORMAL BUTANE ON ACTIVATED CHARCOAL 6 NORMAL BUTANE ON wms PORE SILICAGEL METHANE ON 2 ACTIVATED CHARCOAL l l I l O 2 4 e 8 IO |2|4 :e|e2o22242e2e PRESSURE, PSIA Frez? {aunt ro 0 man Charles W. SkorsrromChester L. Read By 7?, m 3 ,HQALLAL Patent Attorney March 1, 1966 F. H.KANT ETAL 3,237,379

ADSORPTION SYSTEMS IN HEATLESS FRACTIONATION PROCESSES Filed Feb. 26,1962 5 Sheets-Sheet 4 0 In "LR is ru 0 mon Charles W. Skors'rrom'nVemOrs Chester L. Read y R g oln-J K "'K PqfenfAfl'om y AllOVdVODISNIHlNI "IVLLINI d0 loAllOVdVO .LN388OSOV "IVOOHVHO GHJVMlOV x I x x xx xoQ X X I K x x P J r J J S. o PE 5 5: ER w ol March 1, 1966 F. H.KANT ETAL 3,237,379

ABSORPTION SYSTEMS IN HEATLESS FRACTIONATION PROCESSES Filed Feb. 26.1962 5 Sheets-Sheet 5 PRIMARY EFFLUENT I E FF'LUENT 32 FIG. 5

71 'EATS AN CHARLES w. SKARSTROM 'NVENTORS cuss-ran u... READ UnitedStates Patent 3,237,379 ABSORPTION SYSTEMS IN HEATLESS FRACTIONATIONPROCESSES Fred H. Kant, Cranford, N.J., Ira B. Goldman, Takoma Park,Md., and Charles W. Skarstrorn, Montvale, and Chester L. Read,Westfield, N.J., assignors to Esso Research and Engineering Company, acorporation of Delaware Filed Feb. 26, 1962, Ser. No. 175,710 4 Claims.(Cl. 55-58) The present invention is concerned with an improvedadsorption system in heatless fractionation processes wherein amulticomponent mixture in the vapor phase is separated into two streamshaving different physical properties. More specifically, the presentinvention is concerned with an improved adsorption system wherein asubstantially pure component is obtained from a multicomponent mixturestream by heatless fractionation in the vapor phase using high pressureadorption and low pressure desorption.

In its most specific aspect, the present invention is concerned with animproved adsorption system used in a heatless fractionation processwherein a substantially pure component is obtained from a multicomponentmixture by high pressure adsorption and low pressure desorption. Theadsorbent which is used to separate key components from themulticomponent mixture to yield the desired substantially purecomponent, has very high capacity for the other components in themulticomponent mixture and therefore this adsorbent becomes saturatedwith these other more difficultly desorbable components and thus tendsto lose adsorption capacity as the process continues.

In a specific embodiment of the present invention a dual adsorptionsystem is used in the purification of hydrogen from ahydrogen-hydrocarbon mixture wherein the hydrocarbon mixture compriseshydrocarbon compounds having from 1 to carbon atoms.

In the heatless fractionation process it is possible to obtain a highpurity product with relatively high recoveries from the feed streamusingthe high pressure adsorption and low pressure desorption technique.However, when a stream having a broad range of compounds is beingprocessed, the difliculty arises that the adsorbent often exhibits anextremely high capacity for some of the components in the feed stream.

In heatless fractionation there is a term used which defines therelative ease of separation of components which is called the relativevelocity. Thus, with a given adsorption system processing amulticomponent stream the component or components which comprise thedesired product pass through the adsorption zone at a relatively fasterrate than the key component or components. Therefore, it is possible todiscontinue the adsorption portion of the cycle before the key componentor components break through the adsorbent bed into the primary eflluentstream.

In this discussion the primary eflluent stream is the unadsorbed portionof the feed stream which passes through the adsorption zone. The keycomponent or components comprise that portion of the feed streamadsorbed in the adsorption zone.

It often arises that the more desirable component or components arepresent in the feed stream with key components having a broad range ofphysical properties. For instance, the separation of hydrogen fromhydrocarbon compounds is made using activated characoal adsorbent whichappears to adsorb hydrocarbon compounds on a molecular weight basis.Thus, the heavier hydrocarbon compounds are very difiicult to desorbfrom the activated It should be noted that when a broad range ofcomponents is being processed the adsorbent generally loses capacityeven though the normal desorption technique is used, that is,depressuring the adsorption zone to the desorption pressure, and purgingand repressuring the zone with a portion of the primary efiluent. It mayalso be noted that purging the zone with a large volume of primaryeflluent tends to offset the capacity loss of the adsorbent to someextent. Also, a very low desorption pressure helps to reduce thiscapacity loss. However, both of these expedients have practicallimitations. If the purge rate is increased to lower the rate ofcapacity decline a substantial loss in the recovery of the moredesirable components results. This, of course, lowers the efiicieney ofthe process.

With respect to the desorption pressure, there is a practical limitationas to how low a desorption pressure can be obtained. Furthermore, when acombustible gas is being processed a fire hazard arises since air tendsto leak into the system.

Therefore, it is an object of the present invention to provide anadsorption system in a heatless fractionation process wherein there issubstantially no adsorbent capacity decline even though am-ulticomponent stream comprising components with a broad range ofphysical properties is processed.

It is a further object of the present invention to provide a heatlessfractionation process wherein extremely good recoveries of moredesirable components present in the feed stream can be obtained withsubstantially no loss in adsorption capacity.

These objects of the present invention are achieved using multipleadsorbent stages. Adsorbents are selected which exhibit the properaflinity for a component or group of components. By having successivestages of adsorbents, each adsorbent removes a component or group ofcomponents from the feed stream as it passes through the adsorption zoneuntil the final separation is made and the unadsorbeds components aretaken off as primary efll-uent. The adsorbents are restored to initialcapacity by desorbing the components in the steps of depressuring theadsorption zone to the desorption pressure, purging the zone with aportion of the primary eflluent, and repressuring the zone with primaryeffluent.

In the present invention the adsorbents can be in separate fixed bedsconnected by a conduit or they can be in one zone thus being adjacentone to the other.

Other objects and advantages of the present invention will becomeapparent when viewed in light of the accompanying description anddrawings.

FIGURE 1 is a schematic representation of the heatless fractionationprocess employing the present invention.

FIGURE 2 is a graphic illustration of the rate at which an adsorbedcomponent is desorbed.

FIGURE 3 is a graphic illustration of the adsorption isotherm ofn-hexane, n-butane and methane on activated charcoal adsorbent.

FIGURE 4 is a graphic illustration showing the effectiveness of a dualadsorption system of the present invention.

FIGURE 5 is a schematic representation of the heatless fractionationprocess wherein the embodiment employing physically separated adsorbentzones in each bed is shown.

Referring now to FIGURE 1 in more detail, numeral 24 designates the linein which the hydrogen-hydrocarbon mixture feed stream is introduced intothe heatless fractionator. The feed stream in line 24 passes into header25, through valve 27, into line 29 and into adsorption zone 33.

In this description adsorption zone 33 is on the adsorptionportion ofthe cycle and adsorption zone 34 is on the desorption portion of thecycle. The two-zone system herein illustrated contemplates a continuouscyclic process wherein one zone is on the adsorption portion of thecycle and the other zone is on the desorption portion of the cycle. Thefeed stream, which contains hydrogen and hydrocarbon compounds, havingfrom 1 to carbon atoms, passes into adsorption zone 33. The lowerportion of adsorption zone 33 is packed with adsorbent A while the upperportion of adsorption zone 33 is packed with adsorbent B. In thisspecific embodiment of the present invention adsorbent A is a wide poresilica gel adsorbent having an average pore diameter in the range offrom 50 to 500 A. An average pore diameter in the range of from 100 to200 A. is preferred. Adsorbent B is activated charcoal adsorbent. Thus,as the hydrogen-hydrocarbon mixture passes through adsorption zone 33the (2 hydrocarbons are adsorbed on the wide pore silica gel. The C to Chydrocarbon compounds are adsorbed on the activated charcoal adsorbent.A substantially pure hydrogen stream (990+ mol percent) leavesadsorption zone 33 through line 35, valve 41 and into header 43 and isremoved as primary effiuent in line 40. Valve 37 remains closed during aportion of the adsorption period and is opened to allow purging of zone33 and depressuring of that zone during the desorption portion of thecycle.

As previously mentioned, adsorption zone 34 is on the desorption portionof the cycle. Initially, zone 34 is at the adsorption pressure. Zone 34is depressured by opening valve 30 so that the vapor in adsorption zone34 passes through line 28, valve 30 and into header 32 where it iswithdrawn as secondary effiuent. Following the depressuring step,adsorption zone 34 is purged with a portion of the primary effluent inline 40.

The purge passes from line 40 through header 39, valve 38, line 36 andinto adsorption zone 34. Both adsorbents in zone 34 are backwashed withpurge. From adsorption zone 34 it passes through line 28, valve 30,header 32 and is withdrawn as secondary efiluent. Following the purgestep, adsorption zone 34 is repressured to the adsorption pressure withprimary eflluent.

The repressuring step is accomplished by closing valve 30. With valve 38open the primary efiluent passes from line. 40 into header 39 throughvalve 38 into line 36 and into adsorption zone 34. When adsorption zone34 has been repressured to substantially the adsorption pressure, valve'38 is closed and adsorption zone 34- is then ready to be put on theadsorption portion of the cycle. During the adsorption portion of thecycle the primary effluent from zone 34 is removed by means of line 36,valve 42, {leader 44, and is withdrawn as primary efliuent through ine40.

Adsorption zone 33 is switched from the adsorption portion of the cycleto the desorption portion of the cycle by closing valves 27 and 41 andopening valve 31. Adsorption zone 34 is switched from the desorptionportion of the cycle to the adsorption portion of the cycle by openingvalves 26 and 42.

The adsorption temperature is generally the ambient temperature.However, it is within the scope of the present invention that this vaporphase separation occur either above or below that of the ambient. Sincethis is a heatless fractionation process, it is unnecessary to add heatto desorb the components on the adsorbent. This is accomplished bydepressuring and then purging the adsorbent with primary effluent at lowpressure. The adsorption pressure need not be limited except to theextent that the process of the present invention performs the separationin the vapor phase. Therefore, the combination of adsorption temperatureand, adsorption pressure should be such as will yield a vapor stream atthe adsorption conditions.

The desorption pressure must necessarily be below the adsorptionpressure. This may be either above or below atmospheric pressure. Thedesorption temperature is substantially the same as the temperature ofadsorption.

As previously mentioned, prior art heatless fractionation techniqueshave encountered the difficulty that the adsorbent loses capacity whenprocessing a feed stream having a wide range of different physicalproperties. However, in the process of the present invention no capacityloss is experienced since each adsorbent adsorbs only those componentswhich can be readily desorbed.

In the specific embodiment of the present invention, the primaryseparation between hydrogen and methane takes place in the activatedcharcoal adsorbent portion of the adsorption zone. A secondaryseparation, however, takes place on the wide pore silica gel adsorbent.The C hydrocarbon compounds are removed from the feed stream on the widepore silica gel adsorbent. The quantity of wire pore silica geladsorbent must be such that during the adsorption portion of the cycle,which is in the range of from 1 to 30 minutes, the preferred range beingfrom 3 to 10 minutes, substantially no 0 hydrocarbon compounds reach theactivated charcoal adsorbent. The quantity of activated charcoaladsorbent in adsorption zone 33 and 34 must be such that during theadsorption portion of the cycle substantially no methane will breakthrough into the substantially pure hydrogen stream which is taken offas primary effluent.

While this specific process has been described using the conventionaldepressuring, purging and repressuring techniques, other techniquesknown to those skilled in the artto improve the recovery of the moredesirable components from the feed stream can be used. Some such methodsare upflow depressuring pressure equalization between the two adsorptionzones and upfiow expansion of the gas trapped in the adsorption zone tobackwash the zone.

As thus described the multiple adsorbent adsorption zone has been shownto be a single unit. However, it is within the scope of the presentinvention to provide the different adsorbents in substantially isolatedcompartments. As applied to the system specifically illustrated, thewide pore gel adsorbent is in a bed distinct from the activated charcoaladsorbent. Thus, in the desorption portion of the cycle, the wide poresilica gel adsorbent is depressured first. Then, after the wide poresilica gel adsorbent is depressured to the low desorption pressure, the.activated charcoal adsorbent is depressured through it. Thus a purgingeffect is obtained as a result of the depressuring of the activatedcharcoal adsorbent through the wide pore silica gel adsorbent. Thistends to increase the efficiency of operation of the wide pore silicagel adsorbent. Both adsorbents are purged with a portion of the primaryeffiuent at the low desorption pressure.

The present invention is based primarily on selecting the properadsorbents to perform the desired separation. 'In he-atlessfractionation processes taught by the prior art, any adsorbent showingselectivity for the key components in the feed stream would perform asatisfactory separation. It is true that a separation can be performedusing conventional adsorbents. However, in order to obtain optimumrecoveries of the more desirable components from the feed stream it isnecessary to employ adsorbents which can perform the desired separationand still have the characteristic of being readily stripped of theadsorbed components. Therefore, an important concept of the presentinvention is that of the desorption mechanism.

FIGURE 2 graphically illustrates the quantity of n-butane stripped fromactivated charcoal adsorbent as a function of the standard cubic feet ofstripping gas per pound of activated charcoal adsorbent. These data wereobtained with flow rates of either hydrogen or nitrogen stripping gasvarying from 1-15 s.c.f./hr. They were also obtained with varyingadsorbent particle sizes in the range of 10-100 mesh. Furthermore, thestripping data also cover experiments with varying bed diameters from 8mm. to mm. The fact that the stripping data all correlate with theamount of stripping gas passed over the system, and not the rate atwhich this gas is intro duced, means that the mechanism controlling thedesorption is the equilibrium between adsorbate and adsorbent.

It may therefore be visualized that the desorption occurs in thefollowing manner. When a stripping gas, such as nitrogen or hydrogen, ispassed through an adsorbent bed saturated with n-butane, an immediateequilibrium is set up between the gas and the adsorbent such that thepartial pressure of n-butane in the gas phase is that dictated byequilibrium based on the amount adsorbed. In order to establish thisequilibrium, some n-butane is removed from the adsorbent. As a result, anew concentration of adsorbed material on the adsorbent is reached. Thisnew concentration corresponds to a new partial pressure in the gas phaseat equilibrium, which will be lower than the partial pressure at thestart of the desorption period. This process of desorption continuesalways following the equilibrium relation between adsorbed material andpartial pressure in the vapor phase. Since the partial pressure isalways governed by the amount adsorbed, and since the partial pressuredetermines the concentration of the adsorbed material in the vaporphase, the total amount stripped from the adsorbent is simply determinedby the total quantity of gas available during the desorption step. Thisthen explains why the desorption rate is simply a function of the amountof stripping gas passed through the system.

FIGURE 3 graphically illustrates the adsorption isotherms of n-hexane,n-butane and methane on activated charcoal adsorbent. Also, theadsorption isotherm of n-butane on wide pore silica gel is shown forcomparison. In this figure the quantity of component adsorbed in gramsper 100 grams of adsorbent is plotted as a function of the partialpressure of the component in the vapor phase over the adsorbent. Theseadsorption isotherms are obtained by passing the component through theadsorbent bed until adsorption equilibrium is obtained at the givenpressure level. The weight increase of the adsorbent is then measured todetermine the quantity of component adsorbed. The isotherms forn-hexane, n-butane and methane on activated charcoal were ob tained at atemperature of 77 F. The isotherm for n-butane on wide pore silica gelwas obtained at a temperature of 100 F.

Looking first at the adsorption isotherms for three compounds onactivated charcoal adsorbent, it will be noted that the methane isothermis the only one which is substantially linear. Furthermore, it will benoted from the prior art that methane does not contribute to thecapacity loss of activated charcoal adsorbent. That is, methane is notso difiicult to desorb from the activated charcoal adsorbent that ittends to accumulate thereon.

On the other hand, the adsorption isotherm for both n-hexane andn-butane on activated charcoal adsorbents are nonlinear, with then-hexane much more curved than the n-butane. These components bothcontribute to the capacity losses in the activated charcoal adsorbent inthe heatless fractionation process in that they are very difficult todesorb from the adsorbent. Particularly, the n-hexane is more difficultto desorb than the n-butane, which correlates with the degree ofnonlinearity of the adsorption isotherm.

It may also be seen that the adsorption isotherm of n-butane on widepore silica gel is substantially linear. As will be pointed out in moredetail later, the n-butane as well as higher molecular weighthydrocarbon compounds are readily desorbed from the wide pore silica geladsorbent at purge to feed ratios of 1.0.

In this description the purge to feed ratio is taken as the ratio of thevolume of purge at the low desorption 6 pressure to the volume of feedat the high adsorption pressure.

Thus, it has been found that the adsorbents used in the heatlessfractionation process are selected on the basis of the adsorptionisotherm of the components in the feed stream being processed. The merefact that an adsorbent exhibits an aflinity for the components to beadsorbed is not a satisfactory nor sufficient criterion. In order toobtain the maximum recovery of the desired components from the feedstream without incurring the decline in adsorbent capacity with time,the relationship between the adsorbent selected and the component to beadsorbed should be such that all of the adsorbed material will exhibitapproximately a linear adsorption isotherm on the adsorbent in the rangeof partial pressures that these components exhibit in the feed stream.

In the present invention then, adsorbents are selective for thecomponents in the feed stream sought to be adsorbed, and the equilibriumcapacity of the adsorbent is substantially linear with the pressure ofthe adsorbed component at a constant temperature.

N2 flow rates: 6-10 s.c.f./hr.

Adsorption at F., using 40 mm. Hg N01 in N2 at 14.7 p.s.i.a. totapressure.

Stripping at 100 F., with 14.7 p.s.i.a. N2.

Adsorbent particle sizes from 12 to 28 mesh particles.

The data in Table I illustrate the desirability of using wide poresilica gel to adsorb hydrocarbon compounds having from 4 to 10 carbonatoms. These data were obtained by adsorbing n-heptane on the adsorbentsindicated in the first column. The equilibrium capacity of theadsorbents at a partial pressure of n-heptane of 40 mm. mercury and atemperature of 100 F. is shown in the third column. The time required tostrip the n-heptane from the adsorbent using N at a rate of 6 to 10s.c.f./ hr. and a temperature of 100 F. is also shown. All of theadsorbents listed exhibit an aflinity for n-heptane. However, wide poresilica gel, with an average pore diameter of about A., exhibits thedesorption characteristics which recommend it for use in a heatlessfractionation process for the adsorption of hydrocarbon compounds havingfrom 4 to 10 carbon atoms. It may be seen that the wide pore silica gelrequired the smallest amount of purge to completely desorb n-heptane, ofthe :adsonbents shown.

FIGURE 4 is a graphic illustration of the effectiveness of a dualadsorbent comprising 30 wt. percent wide pore silica gel followed by 70vol. percent of HCC activated charcoal, used in a simulated heatlessfractionation cycle to separate hydrogen from hydrocarbon compounds. InFIGURE 4 the methane capacity of the activated charcoal adsorbent in theadsorption zone is plotted as a function of the standard cubic feet ofhydrocarbon feed passed through the zone per pound of activated charcoalin the zone.

The feed composition is 99 vol. percent H and 1% C /C hydrocarbons. Thefeed was obtained by saturating hydrogen with C catalytic reformate at atemperature of 32 F. and 100 p.s.i.g.

The adsorption and desorption conditions were a pressure of 50 p.s.i.g.and a temperature of 100 F. The adsorption and desorption portions ofthe cycle were 6 minutes each. The feed flow rate was about 1.0s.c.f./hr. and the hydrogen purge flow rate was varied from 2 s.c.f./hr.to 0.7 s.c.f./hr. In this manner, various purgeto-feed ratios could beachieved, varying from 2/1 to 0.7/1. The methane capacity of theadsorbent was checked periodically by measuring the time to methanebreakthrough for a 50/50 H /me-thane mixture at 50 p.s.1.g.

The results from the experiments with the dual adsorbent system werecompared to those using only HCC activated charcoal as the adsorbentunder similar process conditions.

It may be seen that with a purge rate of about s.c.f./ hr. the methanecapacity of the adsorption zone packed only with activated charcoalquickly dropped to 60% of its initial capacity at which point itstabilized. This is due to the accumulation of the C hydrocarboncompounds in the feed on the activated charcoal adsorbent. On the otherhand, even with a purge rate of about 1.0 s.c.f./hr., the adsorptionzone packed with 30% Wide pore silica gel and 70% activated charcoal,showed no methane capacity loss.

However, upon reducing the purge rate to 0.7 s.c.f./ hr., a capacitydecline is indicated. This is due to the fact that the concentrationgradient of the components adsorbed on the wide pore silica gel was notswept back as far during the desorption portion of the cycle as it wasswept forward during the adsorption portion of the cycle. The net resultof this was to allow the heavy hydrocarbon compounds to break throughinto the activated charcoal portion of the adsorption zone and bringabout an adsorbent capacity loss.

FIGURE 5 is a schematic description of the specific embodiment of thepresent invention wherein the adsorbent zones in each of the beds arephysically separated. The numbering used in FIGURE 5 is identical tothat of FIGURE 1 except for the added elements indicated below. Zone Aand zone B of bed 34 (indicated as 34A and 34B respectively) areseparated and line 47 and valve 45 are interjected between them. Duringdepressuring, valve 30 is opened while valve 45 is closed therebyallowing zone A to be depressured independently of zone B. Subsequently,valve 45 is opened and zone B is depressured through zone A.

Line 48 and valve 46 perform the respective same functions for zones Aand B of bed 33 (indicated as 33A and 33B respectively).

Thus, in the multiple adsorbent system of the present invention, thequantity of each adsorbent must be such that the concentration gradientof the adsorbed components stays within the physical bounds of eachadsorbent type. Furthermore, at steady state, the concentration gradientof the adsorbed components on each adsorbent is swept backward duringthe desorption portion of the cycle as far as it is swept forward duringthe adsorption portion of the cycle. Thus, there is an oscillatingconcentration gradient of the adsorbed components on each adsorbent.

The adsorbents are staged in series so that each adsorbs only thosecomponents in the feed stream which exhibit a substantially linearadsorption isotherm.

While the present invention has been described with particularity towardthe separation of hydrogen from a mixture of hydrocarbon compoundshaving from 1 to carbon atoms, it will become apparent to one skilled inthe art that the process of the present invention is applicable to anysituation wherein a stream of several components having a wide range ofphysical properties is fractionated in the vapor phase. Unless otherwiseindicated, the previously described experimental illustrations of thepractice of the present invention were conducted in a system whereineach adsorption vessel was one inch in diameter by five feet in length.

Having described this invention, what is sought to be protected byLetters Patent is set out in the following claims.

What is claimed is:

1. Process for the heat ess fractionation separation of hydrogen from agaseous feed stream comprising hydrogen and hydrocarbon compounds whichcontain about 1 to 10 carbon atoms, said process utilizing twoadsorption zones to which no heat is added or removed during theprocess, said two adsorption zones being characterized by having a oneend and another end, said process comprising the steps of flowing saidfeed stream from one end to the other end through a first zone ofadsorbents, consisting of a first bed of silica gel adsorbent having anaverage pore diameter in the range from about to 200 Angstrom units anda second bed of activated charcoal adsorbent initially relatively freeof said hydrocarbon compounds, at a preselected, initial relatively highpressure in an initial cycle, said beds being arranged in the adsorptionzone in such manner that the silica gel adsorbent is adjacent said oneend and said activated carbon adsorbent is adjacent said other end, saidadsorbents being preferentially selective for said hydrocarboncompounds, discharging a hydrogen-enriched stream from said first zoneas a primary effluent, segregating a portion of said primary efiluent asa product stream and withdrawing the same, passing the remainder of saidprimary effluent from the other end to the one end through a second zoneof adsorbents at a relatively low pressure, said second zone ofadsorbents consisting of a first bed of silica gel adsorbenthaving anaverage pore diameter in the range from about 100 to 200 Angstrom unitsand a second bed of activated charcoal adsorbent, the adsorbents beingarranged in said second zone in such manner that said silica geladsorbent is adjacent said one end and said activated carbon adsorbentis adjacent said other end, said adsorbents in said second Zone beingrelatively saturated with said hydrocarbon compounds as compared withsaid first zone at the start of said initial cycle, whereby as saidinitial cycle continues, said first zone becomes relatively saturatedwith said hydrocarbon compounds progressively from said one end towardsaid other end, and whereby said second zone becomes relatively free ofsaid hydrocarbon compounds from said other end toward said one end,continuing said initial cycle for a time period less than that requiredto secure saturation of said first zone at said other end With saidhydrocarbon compounds and that required to secure freedom from saidhydrocarbon compounds of said second zone at said one end, thereafterintroducing said feed stream into said one end of said second zone atsaid initial relatively high pressure, discharging said gaseous mixturestream from said other end of said second zone as a hydrogen-enriched,primary efiluent, segregating a portion of said last-named primaryeffiuent as a product stream and withdrawing the same, passing'theremainder of said last-named primary effluent from said other end tosaid one end through said first zone at relatively low pressure, saidrelatively low pressures in the respective zones being attained byreducing the pressure initially at said one end whereby said silica geladsorbent is depressurized first and said activated carbon adsorbent isdepressurized secondly, thereafter cyclically continuing the operation,and wherein the silica gel adsorbent is present in each said zone insufiicient quantity so as to prevent the breakthrough of C hydrocarbonsinto the activated carbon adsorbents.

2. The process of claim 1 in which the silica gel adsorbent and theactivated charcoal adsorbent in each of the first and second adsorptionzones are in juxtaposition in a single casing.

3. The process of claim 1 in which the silica gel adsorbent and theactivated charcoal adsorbent in each of the first and second adsorptionzones are in separate casings.

4. The process of claim 3 in which the pressure of the adsorbents in theseparate casings are independently controlled.

(References on following page) References Cited by the Examiner UNITEDSTATES PATENTS Hasche 5558 Ringham et a1. 5562 Plank et a1. 252449 Gray5574 Richmond et a1. 5575 Skarstrom 5562 Vasan et a1 5562 Milton 5s 7s10 Russell 5531 10 Skarstrom et a1. 55-179 Thomas 5575 Dow 5562 X Averyet a1. 5575 X Hoke et a1. 5558 Marsh et a1. 5558 X Vasan 5562 X FOREIGNPATENTS Great Britain.

REUBEN FRIEDMAN, Primary Examiner.

1. PROCESS FOR THE HEATLESS FRACTIONATION SEPARATION OF HYDROGEN FROM AGASEOUS FEED STREAM COMPRISING HYDROGEN AND HYDROCARBONCOMPOUNDS WHICHCONTAIN ABOUT 1 TO 10 CARBON ATOMS, SAID PROCESS UTILIZING TWOADSORPTION ZONES TO WHICH NO HEAT IS ADDED OR REMOVED DURING THEPROCESS, SAID TWO ADSORPTION ZONES BEIG CHARACTERIZED BY HAVING A ONEEND AND ANOTHER END, SAID PROCESS COMPRISING THE STEPS OF FLOWING SAIDFEED STEAM FROM ONE END TO THE OTHER END THROUGH A FIRST ZONE OFADSORBENTS, CONSISTING OF A FIRST BED OF SILICA GEL ADSORBENT HAVING ANAVERAGE PORE DIAMETER IN THE RANGE FROM ABOUT 100 TO 200 ANGSTROM UNITSAND A SECND BED OF ACTIBATED CHARCOAL ADSORBENT INITIALLY RELATIVELYFREE OF SAID HYDORCARBON COMPOUNDS, AT A PRESELECTED, INITIAL RELATIVELYHIGH PRESSURE IN AN INITIAL CYCL SAID BEDS BEING ARRANGED IN THEADSORPTION ZONE IN SUCH MANNER THAT THE SILICA GEL ADSORBENT IS ADJACENTSAID ONE END AND SAID ACTIVATED CARBON ADSORBENT IS ADJACENT SAID OTHEREND, SAID ADSORBENTS BEING PREFERENTIALLY SELCTIVE FOR SAID HYDROCARBONCOMPOUNDS, DISCHARGING A HYDROGEN-ENRICHED STREAM FROM SAID FIRST ZONEAS A PRIMARY EFFLUCENT, SEGREGATING A PORTION OF SAID PRIMARY EFFLUCENTAS A PRODUCT STREAM AND WITHDRAWING THE SAME, PASSING THE REMAINDER OFSAID PRIMARY EFFLUETN FROM THE OTHER END TO THE ONE END THROUGH A SECONDZONE OF ADSORBENTS AT A RELATIVELY LOW PRESSURE, SAID SECOND ZONE OFADSORBENTS CONSISTING OF A FIRST BED OF SILICA GEL ADSORBENT HAVING ANAVERAGE PORE DIAMETER IN THE RANGE FROM ABOUT 100 TO 200 ANGSTROM UNITSAND A SECOND BED OF ACTIVATED CHARCOAL ADSORBENT, THE ADSORBENTS BEINGARRANGED IN SAID SECOND ZONE IN SUCH MANNER THAT SAID SILICA GELADSORBENT IS ADJACENT SAID ONE END AND SAID ACITVATED CARBON ADSORBENTIS ADJACENT SAID OTHER END, SAID ADSORBENTS IN SAID SECOND ZONE BEINGRELATIVELY SATURATED WITH SAID HYDROCARBON COMPOUNDS AS COMPARED WITHSAID FIRST ZONE AT THE START OF SAID INITIAL CYCLE, WHEREBY AS SAIDINITIAL CYCLE CONTINUES SAID FIRST ZONE BECOMES RELATIVELY SATURATEDWITH SAID HYDROCARBON COMPOUNDS PROGRESSIVELY FROM SAID ONE END TOWARDSAID OTHER END, AND WHEREBY SAID SECOND ZONE BECOMES RELATIVELY FREE OFSAID HYDROCARBON COM-